1. Field of the Invention
The present invention relates generally to connectors for terminating the ends of coaxial cables of the general type used in the telecommunications industry, and more specifically, to an improved connector that can easily be soldered onto the end of such a coaxial cable.
2. Description of the Related Art
Coaxial cable is widely used in the telecommunications industry to transport radio frequency signals. Such coaxial cable typically includes a center conductor made of copper for transmitting signals. The center conductor is surrounded by a dielectric material which, in turn, is surrounded by a semi-rigid, metallic outer conductor. The outer conductor may be relatively smooth, or it may be corrugated to enhance or ease bending of the coaxial cable. Typically, the outer conductor is covered by an insulative jacket to protect the outer conductor and to seal out moisture.
It is necessary to electrically and mechanically couple the ends of such coaxial cables to equipment ports or other cables in a system, and end connectors for serving such purpose are known. Examples of such coaxial cable connectors include U.S. Pat. No. 4,854,893 to Morris, and U.S. Pat. No. 4,923,412 to Morris; these patents disclose the use of a ferrule which is mechanically compressed against the outer conductor to clamp the coaxial cable within the connector. These patents also disclose the use of a collet to mechanically seize the center conductor of the coaxial cable and to thereby establish an electrical coupling between the center conductor and the center pin of the connector. Other examples of coaxial cable connectors of this general type include U.S. Pat. No. 6,019,636 to Langham, U.S. Pat. No. 5,352,134 to Jacobsen, et al., U.S. Pat. No. 5,651,698 to Locati, et al.; and U.S. Pat. No. 6,183,298 to Henningsen.
Despite efforts to seal such connectors from the elements, moisture sometimes penetrates into such connectors and corrodes the electro/mechanical contact between the center pin of the connector and the center conductor of the cable, resulting in a loss of signal strength or other signal degradation. Likewise, corrosion can form between the mechanism that clamps the connector to the outer conductor of the coaxial cable, thereby compromising the shielding of the desired signal from interference, and also allowing the signal being conducted to leak out of the cable.
Efforts have been made to avoid such problems by providing connectors that can be soldered onto the prepared end of a coaxial cable. For example, U.S. Pat. No. 5,802,710 to Bufanda, et al. describes a coaxial cable assembly which includes an end connector having a center pin that is soldered onto the end of the center conductor. An insulative disc is inserted over the exposed end of the cable, around the center conductor, before the center pin is soldered onto the exposed end of the center conductor. Bufanda, et al. explain that such insulative disc acts as a xe2x80x9csolder gaugexe2x80x9d by spacing the center pin of the connector at the proper axial distance from the exposed end of the coaxial cable. Pre-formed solder is then applied over the exposed outer conductor, and a body member is inserted over the exposed end of the cable. The body member includes a further insulator having a center hole formed therein for allowing the center pin to extend therethrough, while providing mechanical support to the center pin. A fastening nut is rotatably secured to the body member for fastening the connector to a mating connector. After the body member is slid over the outer conductor, the connector is heated to melt the pre-formed solder to establish a mechanical and electrical connection between the body member and the outer conductor of the coaxial cable. Bufanda et al. explain that the aforementioned insulative disc causes solder pooling to occur between the outer conductor and the body member at the location of the insulative disc to create a circumferential seal therebetween.
The connector described by Bufanda et al. requires the use of both an insulative disc and a second insulator to support the center pin within the body member. The need for two such insulators increases the cost of such connector. Moreover, the connector described by Bufanda et al. relies entirely upon the solder connection between the outer conductor of the coaxial cable and the body member to maintain mechanical coupling between the connector and the coaxial cable. Mechanical stress applied to such solder joint, due for example to pulling forces and/or bending forces at the connector/cable junction, can compromise the mechanical and electrical coupling between the outer conductor of the coaxial cable and the body member, and can degrade the moisture seal formed therebetween. In addition, the single mechanical support, formed at the solder joint between the outer conductor of the cable and the body member, tends to act as a fulcrum or pivot point; movement of the coaxial cable behind the connector is thereby transmitted, via the center conductor, to the center pin of the connector, resulting in movement at the connector interface. Such movement at the connector interface causes electrical performance instability and intermodulation distortion instability.
Accordingly, it is an object of the present invention to provide a coaxial cable connector that can be easily and conveniently soldered onto the end of a coaxial cable.
It is another object of the present invention to provide such a coaxial cable connector which allows the user to solder the body of the connector to the outer conductor of the coaxial cable, and which optionally allows a user to solder the center pin of the connector to the center conductor of the coaxial cable.
Still another object of the present invention is to provide such a coaxial cable connector which prevents excess solder from flowing into the body beyond the end of the outer conductor of the coaxial cable.
Yet another object of the present invention is to provide such a coaxial cable connector with improved pull-off strength.
A further object of the present invention is to provide such a coaxial cable connector that captures the cable jacket to prevent the possibility of it shrinking, or pulling back, thereby maintaining moisture seal integrity.
A still further object of the present invention is to provide such a coaxial cable connector with enhanced electrical and intermodulation distortion stability.
Another object of the present invention is to provide additional mechanical support between the coaxial cable and the connector to eliminate the above-described fulcrum/pivot action of the solder joint formed between the outer conductor of the cable and the body of the connector.
A still further object of the present invention is to provide such a coaxial cable connector with an improved seal between the body of the connector and the coaxial cable jacket to reduce moisture penetration and related corrosion-induced reliability problems.
A yet further object of the present invention is to provide such a coaxial cable connector that is less subject to mechanically induced stress and strain due to bending of the coaxial cable near the rear of the connector.
These and other objects of the present invention will become more apparent to those skilled in the art as the description of the present invention proceeds.
Briefly described, and in accordance with a preferred embodiment thereof, the present invention relates to a solder-on connector for a coaxial cable and including a body member having a first end with an internal bore formed therein to provide a generally cylindrical cavity for receiving an exposed end of a coaxial cable, and a coupler secured to the second opposing end of the body member to removably fasten the connector to a mating coaxial connector; this coupler could take the form of a rotatable internally-threaded coupling nut, a rotatable externally-threaded member, a bayonet-style rotatable coupler, or the like. Alternatively, the coupler could be fixedly-secured to the second end of the body member, in the form of external threads formed upon the second end of the body member for mating with a rotatable nut on a mating component, or bayonet-stylexe2x80x9cearsxe2x80x9d formed upon the second end of the body member for mating with a rotatable connector of a mating component. On the other hand, the coupler could simply be a flange formed upon the second end of the body member, the flange extending generally perpendicular to the body member and having mounting holes formed around the outer periphery thereof for receiving mounting screws or bolts used to secure such flange to a similar flange of a mating component. As used herein, the terms xe2x80x9ccouplerxe2x80x9d and xe2x80x9cfastenerxe2x80x9d could include all of such coupling mechanisms and their equivalents.
The solder-on connector of the present invention also includes an insulator that is received within the generally cylindrical cavity of the body member. This insulator extends between first and second ends relative to the longitudinal axis of the body member. The first end of the insulator has a generally cylindrical outer wall having an outer diameter generally commensurate with the internal diameter of the bore formed in the first end of the body member. The first end of the insulator is adapted to abut an exposed edge of the outer conductor of a coaxial cable inserted within the first end of the body member. The second end of the insulator has a central aperture extending therethrough that is generally coaxial with the longitudinal axis of the body member. The solder-on connector further includes a pin having a first end for engaging the center conductor of the coaxial cable, and having an opposing second end which extends outwardly through the aperture formed in the second end of the insulator. The pin is, at least in part, supported by the aperture formed in the second end of the insulator, thereby centering the pin with the longitudinal axis of the body member.
Preferably, the first end of the pin has a bore formed therein for receiving an exposed end of the center conductor of the coaxial cable. In the preferred embodiment of the invention, a solder joint is formed between the first end of the pin and the exposed end of the center conductor.
It was mentioned above that among the objects of the present invention are to provide such a coaxial cable connector with improved pull-off strength, enhanced electrical performance instability and intermodulation distortion stability, an improved seal between the body of the connector and the coaxial cable jacket, and reduced susceptibility to mechanically induced stress and strain due to bending of the coaxial cable near the first end of the connector. To such ends, the present invention preferably includes an outermost region located at the first-end opening of the body member, the outermost region having an internal diameter that exceeds the inner diameter of the aforementioned bore formed in the first end of the body member, and which exceeds the outer diameter of the outer protective jacket of the coaxial cable. Consequently, this outermost region of the body member is adapted to receive a portion of the protective jacket of the coaxial cable. Preferably, the inner diameter of this outermost region is joined with the generally cylindrical cavity of the body member by an inwardly tapered wall. Also in the preferred embodiment of the present invention, the outermost region of the body member includes an inwardly directed flange proximate the first end of the body member.
The protective jacket of the coaxial cable is typically made of a thermoplastic material having a characteristic reflow temperature at which it deforms. When the body member of the connector is heated to solder the body member to the outer conductor of the coaxial cable, the portion of the protective jacket received within the outermost region of the body member xe2x80x9cmeltsxe2x80x9d; at this time, the inwardly directed flange of the outermost region of the body member serves to capture melted portions of the protective jacket of the coaxial cable when the same is heated to its characteristic reflow temperature. When the connector cools, the melted portions of the protective jacket solidify, forming a strong supportive joint between the protective jacket and the outermost region of the body member. Those skilled in the art will appreciate that the aspect of applicant""s invention relating to the capture of melted portions of the protective jacket within the outermost region of the body member can be used to advantage whether or not the center conductor of the coaxial cable is actually soldered to the center pin of the solder-on connector.
The insulator used to support the pin within the body member can assume different shapes. For example, the insulator can be generally shaped like a cup, with the xe2x80x9cmouthxe2x80x9d of the cup facing the exposed end of the coaxial cable, and the centering hole being formed in the xe2x80x9cbasexe2x80x9d of the cup. In this case, the generally circular outer wall of the cup-shaped insulator is spaced apart from, and surrounds, the first end of the pin. Alternatively, the insulator can be a solid, or partially-solid, cylinder, or it may be generally conical, with the xe2x80x9cbasexe2x80x9d of the cone facing the exposed end of the coaxial cable, and the peaked end of the cone being directed toward the second end of the body member for supporting the pin.
Regardless of the shape of the insulator, if the pin of the connector is to be soldered onto the center conductor of the coaxial cable, then the insulator preferably extends along the longitudinal axis of the body member for a length that is greater than one-half of the internal diameter of the generally cylindrical cavity formed in the first end of the body member. Thus, if the insulator is cup-shaped, then the height (or length) of the cup is preferably at least one-half of its maximum diameter. It is preferred that the centering hole formed in the second end of the insulator be commensurate with the diameter of the pin to result in a press fit between the pin and the insulator. As the insulator is press fit over the pin, the first end of the insulator is preferably advanced at least as far as the first end of the pin along the longitudinal axis of the body member.
Another aspect of the present invention relates to a method of forming a solder-on end connector, of the general type described above, upon an exposed end of a coaxial cable, wherein both the center conductor of the coaxial cable and the outer conductor of the coaxial cable are joined by solder to the end connector. To practice such method, a pin is provided having first and second ends, the first end of the pin having a central bore. The exposed end of the center conductor of the coaxial cable is inserted into the central bore of the first end of the pin. The first end of the pin is soldered to the center conductor of the coaxial cable. An insulator is provided having a first end that includes a generally cylindrical outer wall having an outer diameter; the second opposing end of the insulator has a central aperture. The insulator is inserted over the second end of the pin, via the center aperture, until the first end of the insulator abuts an exposed edge of the outer conductor of the coaxial cable. A body member is provided having first and second opposing ends, the first end of the body member including a first-end opening leading into a generally cylindrical cavity having an internal diameter commensurate with the diameter of the outer conductor of the coaxial cable. The first end of the body member is inserted over the exposed end of the coaxial cable, over the second end of the pin, and over the insulator. Solder is applied between the outer conductor of the coaxial cable and the generally cylindrical cavity of the body member. The solder is heated to couple the outer conductor of the coaxial cable with the body member.
Preferably, the step of providing the body member includes the step of forming an outermost region within the first end of the body member, wherein the internal diameter of such outermost region exceeds the inner diameter of the generally cylindrical cavity. In this case, the step of sliding the first end of the body member over the exposed end of the coaxial cable includes the step of sliding the outermost region of the body member over the protective jacket of the coaxial cable to allow a portion of the protective jacket to enter such outermost region. Assuming that the protective jacket of the coaxial cable is made of a thermoplastic material having a characteristic reflow temperature at which it deforms, then the aforementioned step of heating the solder to couple the outer conductor of the coaxial cable with the body member includes the further step of heating the protective jacket to its characteristic reflow temperature for melting portions of the protective jacket within the outermost region of the first end of the body member. To further ensure a secure connection between the protective jacket and the outermost region of the body member, the step of forming such outermost region preferably includes the step of forming an inwardly directed flange within such outermost region proximate the first end of the body member for capturing melted portions of the protective jacket of the coaxial cable when the same is heated to its characteristic reflow temperature during the soldering step. Those skilled in the art will appreciate that the central pin of the connector need not necessarily be soldered to the center conductor of the coaxial cable, in which case, the central pin, surrounding insulator, and body member can be pre-assembled.
In practicing the above-described method, the step of applying solder between the outer conductor of the coaxial cable and the body member can be performed in a number of different ways. For example, the step of applying such solder may include the step of applying solder paste within the body member before sliding the body member over the pin, insulator, and coaxial cable. Likewise, the step of applying such solder may include the step of applying solder paste onto the outer conductor of the coaxial cable before sliding the body member over the pin, insulator, and coaxial cable. Alternatively, such solder might be provided by applying pre-formed solder onto the outer conductor of the coaxial cable before sliding the body member over the pin, insulator, and coaxial cable.